This invention relates to mixtures of pentafluoropropane and a hydrofluorocarbon having 3 to 6 carbon atoms. These mixtures are useful as refrigerants for heating and cooling.
Fluorocarbon based fluids have found widespread use in industry for refrigeration applications such as air conditioning and heat pump applications. Vapor compression is one type of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
The primary purpose of refrigeration is to remove energy at low temperature. The primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because, for heating, the operation of the condenser is interchanged with that of the refrigeration evaporator.
Certain chlorofluoromethane and chlorofluoroethane derivatives have gained widespread use in refrigeration applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties. The majority of refrigerants utilized in vapor compression systems are either single component fluids or azeotropic mixtures. Moreover, certain applications, such as centrifugal chillers, can only use pure or azeotropic refrigerants because non-azeotropic mixtures will separate in pool boiling evaporators resulting in undesirable performance. In other applications, non-azeotropic (or zeotropic) refrigerants may be used.
Azeotropic or azeotrope-like compositions are particularly desirable because they do not fractionate on boiling. This behavior is desirable because in the vapor compression equipment in which these refrigerants are employed, condensed material is generated in preparation for cooling or heating purposes. Unless the refrigerant composition exhibits a constant boiling point, i.e., is azeotrope-like, fractionation and segregation will occur on evaporation and condensation producing undesirable refrigerant distribution which may upset the cooling or heating. If a leak occurs in a refrigeration system during use or service, the composition of the azeotrope-like mixture does not change and, thus, the system pressures and performance remain unaffected.
The art continually seeks new fluorocarbon based azeotrope-like as well as zeotropic mixtures that offer alternatives for refrigeration and heat pump applications. Currently of interest are fluorocarbon based mixtures that are considered to be environmentally safe substitutes for the fully halogenated chlorofluorocarbons (CFC""s) presently used that are suspected of causing environmental problems in connection with the earth""s protective ozone layer.
The substitute material must also possess those properties unitize to the CFC""s being replaced including chemical stability, low toxicity, non-flammability, and efficiency in use. The latter characteristic is important in refrigeration and air conditioning especially where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel use arising from an increased demand for electrical energy. Furthermore, the ideal CFC refrigerant substitute would not require major engineering changes to conventional vapor compression equipment currently used with CFC refrigerants.
Mathematical models have substantiated that hydrofluorocarbons such as pentafluoropropane, including 1,1,2,2,3-pentafluoropropane (HFC-245ca), 1,1,2,3,3-pentafluoropropane (HFC-245ea), 1,1,1,2,3-pentafluoropropane (HFC-245eb), and 1,1,1,3,3-pentafluoropropane (HFC-245fa) will not adversely affect atmospheric chemistry because these hydrofluorocarbons are negligible contributors to ozone depletion and to xe2x80x9cgreen-housexe2x80x9d global warming in comparison to fully halogenated species.
However, 245eb has been found to have flame limits under normal ambient conditions and HFC-245ca and HFC-245fa have been found to have flame limits under certain conditions. It has not been confirmed whether or not the other pentafluoropropane isomer also exhibits some finite flame propagation behavior in specific environments. This flame propagation behavior would significantly limit the potential use of pentafluoropropane isomers in refrigerant applications.
In accordance with this invention, novel mixtures have been discovered comprising pentafluoropropane (HFC-245) and a hydrofluorocarbon of the formula CxFyHz wherein x is 3, 4, 5, or 6 and y and z are each independently 1 or a positive whole number such that the product of y/(y+z) is greater than 0.67. Preferably, the 245 isomer is either 245ca or 245fa, most preferably 245fa. A second aspect of this invention is a cooling process in which any of the refrigerants of this invention are condensed and then evaporated in the vicinity of an object to be cooled. Additionally, the same process may be used to heat an object in the vicinity of the condensing refrigerant. Both the heating and cooling processes may be characterized as processes for transferring heat by condensing the refrigerant in a first region to be heated, transferring the refrigerant to a second region to be cooled, and evaporating the refrigerant in the region to be cooled.
The compositions of the invention comprise, consist essentially or consist of azeotrope-like or zeotropic mixtures. Azeotrope-like characteristics are inherent in those compositions in which an azeotropic system exists. In such systems, the precise azeotropic compositions have not been determined but have been ascertained to bewithin the ranges indicated herein. In general, in such systems, the azeotrope-like compositions exhibit vapor pressures within about xc2x15 psia and preferably within about xc2x12 psia (at 0xc2x0 C.) of the vapor pressure of the true azeotrope (at 0xc2x0 C.).